Insulation for electrical apparatus



July 21, 1936- A. o. AUSTIN INSULATION TOR ELECTRICAL APPARATUS original Filed Maron 5, 1931 T A I l/ Patented July 21, 1936 INSULATION Fon ELECTRICAL APPARATUS Arthur 0. Austin, near Barberton, Ohio, assignor,

by mesne assignments, to The Ohio Brass Comgany, Manseld, Ohio, a corporation of New ersey Original application March 5, 1931, Serial No.

c have a substantially constant specific inductive stant as possible. Capacity. It is well known that a. filling medium such as A further object of the invention is to increase transformer oil Will take up water, which in turn the specific inductive Capacity of filling material will affect its specific inductive capacity matefor capacitance couplings. rially. While an increase in the specific inducio A further object is to provide filling material tive -capacitycf the oil is produced when the oil for capacitance couplings which will be less aftakes up water, this may'be an advantage insofected by moisture than material heretofore used. far as the capacitance coupling is concerned but A further object is to provide means for Overthe presence of water in the oil lowers its dieleceoming the effect of changes in temperature on tric strength 'and may interfere with the perl5 capacitance couplings. formance of the bushing, particularly if the 15 A further object is to provide a device of the bushing is subjected to very high voltagesclass named which shall be of improved construc- .A change 1n the effective specific inductive ca tion and Operation. pacity of the zones formed by the filling medium Other Objects and advantages Will appeal from will of course change the characteristics of the the following description. capacitance coupling. This, as well as the eect 20 The nVentiOn is exemplified by the eombillalof' different temperatures, will tend to cause vthe tion and arrangement of parts shown in theV accapacitance coupling to vary, making it less suiteelnpanyng drawing and described in the OUOW- able where accuracy is required over a consider'- ine specification, and it is more particularly able period cf time. This applies particularly pointed Out in the appended ClamS- where a close regulation is required, and ln cases 25 This is a division 0f apDhCatiOn Serial Num where voltage or energy is supplied by capaciber 520,285, filed March 5, 1931 now Patent No. tance couplings for relay operation, metering or 1,981,716, dated NOVBmbeI' 20, 1934. other purposes,

In the draWing In order to provide increased energy from the The ligure is an elevation With parts in Section capacitance coupling, to reduce the volumetric 30 of a bushing insulator having one embodiment change in the illing medium and to prevent of the present invention applied theretO- change in `the capacitance of the capacitance In oil filled bushings, particularly those used t coupling caused by change in the specmc inducfor high Voltage, there may be, at times, can aptive capacity of the filling medium when water preciable volumetric change in the oil or lnsulatis absorbed or lost by the filling medium, the 35 ing Compound due to Changes in temperature present invention contemplates the use of a sup- This is particularly true in the `ease 0f bushings plemental dielectric or filling medium which will for transformers of a conservator type where the reduce the quantity of the lliquid filling medium lower ends of the bushings are 'subjected t0 the in the zone affecting the dielectric strength and 40 hot oil on the inside of the transformer housing. capacitance coupling. In general, this can be 40 l Roof or entrance bushings and their contents accomplished by illling the space largely with may be heated to a very large extent by heat insulating bames of material such as porcelain, from the Sun. As the Oil 0r insulating compound glass or othersubstance which will not take up in the bushing has-a rather large volumetric or lose water. For manufacturing reasons, howexpansion compared to the material forming the ever, it is difilcult to fill with baffles all of the 45 shell of the bushing, it is necessary t0 make prO- space between the metallic surfaces which have a vision for this variation in volumetric expansion diner-ence in potential. It is generally advisable either by the use 0f expansion reservoirs 01' eX- to allow some space between the parts to provide panSOn Space in the bushngfor irregularities, and 'also for an insulating me- 1f the amount of oil can be reduced, the amount, dium which will provide insulation even in case 50 of space required for expansion in the bushing, some of the insulating sleeves or bafiles are vbroken or the size of the expansion reservoirs may be or damaged. materially reduced, thereby reducing the cost One method of improving the characteristics and size of a bushing for a. given performance. andthe advantages outlined above is to ll the In bushings in which a capacitance coupling is space between the baflles with a solid material 520,285, now Patent No. 1,981,716, -dated November 20, 1934. Divided and this application February 2, 1933, Serial No. 654,836

\ 1801811115. (Cl-17H1) Y used, it is important that the amount of oil or This invention relates to capacitance members and dielectric filling material therefor, and has for one'of its objects the provision of dielectric material for capacitance couplings which will filling compound in the bushing be reduced to a minimum so that the electrical characteristics of the electrostatic coupling remain as nearly conmade up in small pieces. This will displace a large part of the liquid filling medium and at the same time the specific inductive capacity of the dielectric in the lled space may be materially increased, providing the solid filling material has a. higher specific inductive capacity than the liquid filling medium displaced. The solid material used for filling may be sand, or pieces composed of glass, porcelain or other material which has a higher specific inductive capacity than the liquid filling medium displaced.

The specific inductive capacity of -the material used for filling materal can be-utilized to distribute or control the stress in the various zones in the bushing. If a zone of high stress is filled in with material having a higher specific inductive capacity than the liquid dielectric displaced, the stress over this zone will be reduced. Tre filling material may therefore be used to control the distribution of stress in the bushing as well as to control the effective capacitance, and to reduce the amount of liquid filling material required for filling in the voids or interstices.

By using a filling material which has pore spaces, it is possible to fill the pore spaces with water or other medium which will materially increase its specific inductive capacity. At the same time the surrounding structure of solid material Will tend to maintain the dielectric strength of the particles so lthat the effective insulation will not be materially interfered with.

As it is exceedingly difficult to remove water or other liquid from material which has very small pore spaces, a porous filling material will tend to retain its moisture and thereby maintain a more constant condition than a filling medium Such as insulating oil, which will take up or give off moisture readily under changes in temperature and humidity of the air with which it is in contact.

It is also possible to use insulating baffles made of refractory or ceramic materials which have pore spaces. This material if filled with Water and immersed in a liquid dielectric medium will have a very high effective insulation and an increased effective specific inductive capacity. It is therefore possible to use insulating baffles as well as granular material having an increased specific inductive capacity in Zones of higher stress such as that adjacent to the centerelectrode in a bushing.

The reduction of stress upon this zone will transfer the electrical stress to other zones, thereby tending to equalize the electricalstress. In addition, the increase ineffective capacitance of the zones subjected to the higher stressdue to position will also increase the effective capacitance and, consequently, the output of the capacitance coupling. v

One advantage of the filling material is that it tends to prevent a discharge under high static stress which would tend to drive away the oil where the electrode surfaces terminate. 'Ihe filling material may also be used to control the surface gradient on the outside of the bushing to an appreciable extent where it is possible to fill zones in such a way that the path of electrostatic flux Will be directed by the filling material.

Several means may be used to control the stability of the insulating baffles, and theKlling material used. By using a material for baffles and filling havingvery small pore spaces the retention of moisture or liquid in the pores which will increase the effective specific inductive capacity will be such that there will be little tendency to change the amount present. In some cases, however, where the pore spaces are relatively large, it may be necessary or advisable to cover the impregnated particles or baffles with a varnish, glaze or other material which will retain the entrapped moisture soit will not change with time. The insulating baffles may be glazed on one surface, which will seal the pores, and the unglazed surface, or openings left in the glaze for impregnating, may be covered with an insulating varnish or other material later. Very fine pore spaces may be equivalent to a pressure of several thousand pounds per square inch, in their effect on the retention of moisture, and if small openings are provided in the glaze, the materialmay be impregnated or largely saturated with water or other medium which will be retained even though conditions change materially. Where the pore spaces are larger, the impregnating may be materially accelerated by placing the whole under a high pressure in the liquid used for impregnating.

The drawing shows one form 0f the invention applied to a transformer, circuit breaker, metering or other bushing. The bushing has a central electrode or conductor I0 and a mounting fiange II. Insulating baffles I2 and I3 are placed between the supporting flange I I and the conductor I0. The insulating baffles are surrounded by shells I4 and I5. The baille I3 carries a sleeve 0r zone I6 of conducting material insulated from the conductor I0 and the flange II and forming a capacitance coupling with the conductor I0. The primary Il of a step-down transformer is connected by a lead I8 to the capacitance member I6, the other terminal of the transformer winding being grounded.

In order to improve the characteristics of the bushing and the capacitance coupling described above, the spaces I9, 20, 2|, and 22 are filled with granular, solid, dielectric material having high specific inductive capacity as described above. In order to provide a grading effect, the material used in zone I9 may have a higher effective specic inductive capacity than the material used in thezone 20. The intervening space or interstices between the pieces of filling material can be filled with an insulating oil or compound of the necessary dielectric properties. The grading of the dielectric stress may have a material economic advantage in the construction of the bushing as a zone having a high stress under normalconditions may have a portion of the stress transferred to other zones by increasing the effective capacitance of the highly stressed zones by means of a filling having higher specific inductive capacity. One method wouldbe to use a porous material in the inner zone I9, a non-porous material in 20 and oil in 2I and 22. The zones could of course be materially changed in size to meet the conditions of design. With this arrangement the zone I9 would have its capacitance increased through the absorption of moisture from the oil which would havebut little or no effect upon the material in zone 20.

As vibration may tend to change the location of the various particles of the granular dielectric material and under some conditions may result in an increase inthe mechanical stress set up between the parts, owing to unequal expansion and contraction, it may be desirable to retain the particles of filling material in a fixed position. `This can be readily accomplished in one of several ways. One method is to coat the pieces of filling material with a varnish, oil or other medium which can be used to stick the particles together after they have set a short time. This may be done by filling the bushing with the granular material and the binding material in liquid form and then drawing off excess binding material and allowing the remainder to harden either by drying or by the application of heat.

Another method is to apply a suitable varnish or oil to the granular particles after they have been impregnated with water and then allowing the varnish or oil to harden. 'I'he coated particles may then be handledin a manner similar to uncoated particles of filling material or sand. After the coated particles are in place in the bushing, the bushing with the filling material may be heated sufiiciently to cause the material to soften and bind the several particles together. This will retain the particles in position and, at the same time, seal the pores and retain the material affecting the specific inductive capacity of the particles. It, of course, is also possible to hold the y insulating bailles in place in the outer shell by the coating material on the several particles so that special holding meansy may be dispensed with.

'I'his is particularly true for some of the smaller Y A conductor elements and a porous dielectric interposed between said element and insulating said elements from each other, said dielectric having the pores thereof filled with water,

3. AIn a condenser or capacitance coupling, spaced conductor elements and a porous dielectric interposed between said elements, said dielectric having the pores thereof filled with water and at least a portion of the surface thereof covered with a coating to retain the water in said pores.

4.l Filling material for housings for electrical apparatus comprising an aggregate of small individual particles of porous porcelain having the pores thereof filled with a substance of higher specific inductive capacity than the material of said particles.

5'. A filling for housings for electrical apparatus vcomprising an aggregate formed of porous dielectric particles, the pores of said particles being filled with water, and an insulating liquid filling the interstices between said particles.

6. A condenser or capacitance coupling comprising spaced conductor elements, and a solid dielectric baille interposed between said elements and insulating said elements from each other, said baille being porous and having the pores thereof filled with water.

7. A 'condenser or electrostatic coupling comprising spaced conductor elements and a solid baille interposed between said elements, said baille being porous and having the pores thereof filled with water, a portion at least of the surface of said baille being covered with coating material to retain the water in said pores.

8. A filling for electrical apparatus comprising solid particles of porous dielectric material, water element.

particles together and for closing the pores of said particles to retain in said pores any liquid that may be therein, said binder being svubstany tially restricted to a surface coating of said particles of such thickness only as will adhere to said particles when said binder is in a liquid state and free to flow away by gravity, and an insulating liquid filling the interstices between said particles.

10. IA filler for electrical apparatus comprising particles of porous dielectric material, thepores of said material being filled with water, a binder holding said particles together and covering the surfaces thereof to retain the waterlin said pores, and an insulating liquid filling the interstices between said particles.

11. The dielectric element of a condenser formed of porous non-combustible dielectric material having the pores thereof filled with a liquid of higher specific inductive capacity than saidy dielectric material. Y

12. The dielectric element of `a condenser comprising porous dielectric material having the pores thereof filled with water. I

13. The dielectric element of a condenser comprising porous dielectric material having the pores thereof filled with water and at least a portion of the surface of said material covered with a coating to retain the water in said pores.

`14. A dielectric baille for-electrical apparatus co rising a plate formedy of porous porcelain having a. liquid in the pores of said porcelain of higher specific inductive capacity than said dielectric material.

15. The dielectric element of a condenser comprising a unitary porous plate of dielectric material having the pores thereof filled with water.

16. A dielectric baille fora condenser comprising a unitary porous plate of dielectric material having the pores thereof filled with water and at least a portion of the surface of said plate covered with coating material to retain the water in said pores. s

17. A dielectric filler for electrical apparatus comprising an aggregate formed of particles of porous material, a binder disposed on the surface of said particles for holding said particles together and for`fclosing the pores of said particles to retain in said pores any liquid that may be therein, said binder being substantially restricted to a surface coating of said particles of such thickness only as will adhere to said particles when said binder is in a liquid state and free to flow, away by gravity. andan insulating liquid ARTHUR O. AUSTIN. 

